Method of making electrical contact members



Sept. 8, 1942. J. K. ELY 2,295,338

METHOD OF MAKING ELECTRICAL CONTACT MEMBERS Original Filed April 13, 1940.

Fig.2.

WITNESSES:

Patented Sept. 1942 UNITED STATES PATENT OFFICE METHOD OF MAKING ELECTRICAL CONTACT MEMBERS James K. Ely, Wilkinsburg, la., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Original application April 13, 1940, Serial No.

329,459. Divided and this application Septem ber 21, .1940, Serial No. 357,701

This invention relates to a method of making electrical contact members.

This application is a division of application Serial No. 329,459 of James K. Ely, entitled on tact members and process of maldng the same, filed April 13, 1940.

Contact members for electrical circuit making ing a mixture of powdered refractory metal with a good conducting metal. Such sintered combinations have not resulted in the expected advantageous contact ,members. This is believed due to the fact that the continuity of the electrical path through the good conducting member has been broken in numerous places by the particles of poor conducting refractory metal.

The object of this invention is to provide for combining refractory metals with good conducting metals to form contact members.

Other objects. of the invention will, in part, be obvious, and will, in part, appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each other and the article possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawing in which:

Figure l is a top plan view of a mold;

Fig. 2 is a side elevational view, partly in section, of a mold and an element formed therein,

in accordance with the teachings of this invention;

Fig. 3 Ba view in perspective of a pair of contact members; Fig.4 is a cross-sectional view of a circumferentially reinforced contact;

Fig. 5 is a cross-sectional view of a contact;

Fig; 6 is a top plan view of a split mold, and

Fig. 7 is an enlarged end view of a modified form of refractory metal spacing.

It is the purpose of the invention to embed refractory metals having good wear resistance and good resistance to sticking within a main base member of a good electrical conducting metal. It is a purpose of the invention to so locate the refractory metal within the contact member so as not to interrupt the continuity of the electrical path through the good conducting metal.

The refractory metals which have been found to provide excellent wear resistance and resistance to sticking are the metals tungsten and molybdenum, particularly in wire or rod form. The members are preferably of an elongated shape with any general cross section. A further characteristic which will be desirable in the refractory members is the property 0f being wetted by molten good conducting metal and with a good bond being formed onsolidiflcation. Accordingly,-

other refractory metals having these general properties may be employed as the equivalents of the refractory metals specifically set forth.

The main body of the contact members is composed of a good conducting metal such, for example, as copper and silver. The properties which are desirable for the main body metals'are good electrical conductivity and low contact drop. Copper and silver base alloys, while they may not' have as good conducting characteristics as pure silver or copper, may be suitable for application in contact members, and it is contemplated to make use of them in this invention.

The copper and silver will not form a good alloy with tungsten and molybdenum since these metals do not form solid solutions. Thus, it is not possible to alloy the good conducting metal with a refractory netal to secure a combination of their desirable properties. It is accordingly necessary to mechanically intermingle selected shapes of each of these groups of metals and by v proper casting or other uniting treatment, form a unitary contact member body.

In order to secure the combined advantages of the good conducting metals, copper or silver, and the refractory metals, tungsten or molybdenum, it is proposed to make electrical contact members embodying elements of the refractory metal in a parallel relation relative to the direction of cure rent flow and extending substantially entirely through a cast bonding base member composed of good conducting metaL. In this way the continuity of the electrical path through the 'good conducting metal is not interrupted by the refractory metal. g

For one method of manufacturing the contact 5'5 member according to the invention, reference 13 made to Figs. 1 and 2 of the drawing. In Fig. 2 a circular shell I constituting a mold in which to cast the good conducting metal is closed at its bottom by a circular blank cap 12 fitting tightly therein. The blank cap I2 has arranged therein a series of indentations I4 for properly spacing the refractory metal wires or rods 22.

In order to use the blank cap I2 more than once, it may be advisable to coat it with a thin layer of graphite,'aluminum oxide, or other re,- fractory mineral which will prevent adherence thereto of the' cast metal. The shell I0 may likewise be treated with a graphite or aluminum oxide to permit of easy withdrawal of the cast contact body.

At the top of the mold I0 is placed a second cap I6, preferably of a size smaller than the mold I0, having a series of perforations ll corresponding to the indentations I4 in the lower cap I2. Preferably the upper cap I6 is elevated somewhat above the shell IB by means of rods or spacing members I8. The gap effected by the use of members I8 provides for escape of gases and for casting of the-copper.

In Fig. l a casting lip or trough 20 in the shell I8 is shown. However, other means may be provided for introducing the molten metal into mold It may be desirable to assemble the refractory rods and the caps I2 and I6 together before introduction into the mold shell I0. In such a case the two caps I2 and I6 may be superimposed with the perforations ll and indentations It matching. The refractory metal wires or rods 22 may be inserted through the perforations into the indentations I4. If the upper cap it is of a size slightly smaller than the internal diameter of the shell Ill, the assembly may be introduced from the bottom of shell I!) and the upper cap it may be lifted up by some suitable means such as a small wire (not shown) attached thereto to a position where rods It may be introduced to prevent its falling down. The cap I2 may be then forced tightly into the bottom portion of shell IE to provide a leak-tight joint.

In some instances it may be advisable to preheat the assembly IIl, I2, 22 and I6 in order to effect the best casting of the good conducting metal therein. Since the member I0 may be several feet in length, preheating the mold will aid in forming a uniform casting.

tended to be in a direction perpendicular to the refractory members 22.

Fig. is a top plan view of one of the contact members 3! after being cut of! from a casting. The contact member 30 comprises a-main body member 24 of a substantially unitary structure having embedded therein a plurality of refractory metal'rods 22 extending substantially entirely Preheatin to a temperature somewhat below I the melting temperature of the copper or silver will be suilicient to ensure a uniform and homogeneous casting about the refractory rods 22.

A ladle of molten copper or silver or their good conducting alloys may be conveyed to the mold Iii and the molten metal poured by lip means 20 into the preheated assembly. The molten metal 24 will flow to the bottom of the mold above blank cap I2 and the level of the molten metal will rise until the top of shell I0 has been reached. Gradual cooling, preferably from the bottom of the mold adjacent the cap I2, will ensure a sound casting in the mold I0.

After the entire casting has been solidified, the upper cap I6 may be withdrawn from the upper ends of therods 22, the bars l8 removed and the lower cap l2 may be forced off. If the shell ID has had its interior surface coated with some refractory mineral such as graphite or aluminum oxide, it will be relatively easy to withdraw the casting therefrom. The cast body may be cut by means of an abrasive wheel into contact members of predetermined length. The cutting is intherethrough. The face visible in Fig. 5 is the face which will be subjected to impact with another similar contact member during the making and breakingof electricalcircuits.

Referring to Fig. 3, there is illustrated a pair of opposed contact members 30 similar to the Fig. 5 construction mounted by means of silver brazing or other suitable welding technique upon a pair of contact arms 32 and 34. Suitable circuit breaker mechanism may be arranged to provide for the separation and contact of the opposed contact members 30 by actuating one or the other of arms 32, 34.

In some instances it may be desirable to reinforce the contact member of Fig. 5 to restrain possible mushrooming of the contact under heavy and repeated circuit making contact. In Fig. 4 the external shell 40 of the contact member 28 is made of some metal having considerable tensile strength such, for example, as beryllium copper, with moderate conducting properties. Other metals, depending on the requirements, may be employed for this shell 40.

In producing the reinforced contact member, the shell 40 of suitable metal is used as the mold I0 in Figs. 1 and 2. In making this embodiment, the refractory mineral employed in Fig. 2 on the interior of the shell member I0 will be dispensed with in order that the cast metal may integrally bond, as shown at 26, throughout the entire' length and with the inner surface of the shell 40. Thus a unitary, well-bonded contact member resistant to mushrooming will be provided.

The'molten good conducting metal bonds well with the refractory metals, tungsten and molybdenum, and in the separate contact members formed from the cast body of Fig. 2 or having the reinforced structure described hereinbefore, will exhibit a solid well-bonded contact unit. Under impact it is found that with the refractory metal members disposed as described and extending through the 'contact member to the backing member or contact arm that the resulting stress will be well distributed in the entire contact member. It is believed that such contact members will exhibit well matchedfaces' whereby the current will be uniformly spread over the entire face of the contact and will not be concentrated in small areas. Moreover the small current in refractory rods 22 will easily enter the good conductor main body in which they are bonded.

The shell mold of Fig. 2 may be constructed according to the arrangement of Fig. 6 for ease in separating the cast body from the'mold where the contact members are to be formed without the circumferential reinforcing ring or shell. The mold illustrated in Fig. 6 comprises two identical halves 36 and 38 united by bolting means 42. The mold of Fig. 6 will be easier to manipulate than the solid cylinder III in Fig. 2.

In order to dispense with the necessity for manually locating refractory rods in indentations I4 of blank cap I2 and the perforations ll of cap I6, other means for spacing the refractory rods may be employed. For example, the modification of Fig. 7 may resorted to in some-instances. In Fig. 'l'the refractory members 22 are woven into a sort of fabric by means of spacedapart woof wires 23', 25. For example, the wires 23 and 25 may be spaced an inch or more from each other along the length of the refractory metal members 22.- The refractory metal fabric made in this way may be rolled up on itself as shown on the. lower part of Fig. 7 until a column of refractory material sufiicient for use in the mold ill of Fig. 2 has been obtained. The wires 23 and 25 will provide adeqnate spacing betweenrefractory rods so that molten copper or silver may penetrate and bond the mass as a whole. Obviously the wires 23 and 25 are selected for size according to the spacing desired between the consecutive refractory wires 22. -In any event the refractory members constitute a minor proportion of the whole cross section of a contact member.

Since certain changes in carrying out the above process and certain modifications in the article which embody the invention may be made without departing from its scope, it is intended that all matter contained in the above description or shown in, the accompanying drawing shall be interpreted as illustrative and not in a limiting sense. Therefore, I desire that my invention be interpreted as broadly as possible and that it be limited only by what is expressly set forth in the following claims.

I claim as my invention:

1. The method of making electrical contact members reinforced about their periphery to resist mushrooming and provided with refractory inserts to resist heat and impact deformation,

- comprising, providing an elongated mold of a predetermined reinforcing metal, the mold having, a longitudinal cavity, placing within the longitudinal cavity a plurality of longitudinal uniformly spaced refractory metal inserts selected from the group of tungsten and molybdenum, preheating the mold and refractory metal inserts contained therein, casting a molten tory metal members to bond the mold and refractory metal members into a unitary body, and severing the mold containing the refractorymetal members in the cast metal perpendicular to the length of the unitary body into contact members of predetermined size, the section of mold severed forming a circumferential reinforcement for the cast metal containing the refractory metal members. g

3. The method of making electrical contact members with refractory metal inserts to resist heat and impact deformation, comprising, in combination, combining a plurality of elongated refractory metal members into a substantially uniformly spaced apart, and parallel relation by means of woof wires, rolling up the refractory metal members as spaced by the woof wires into a stack of predetermined shape, providing a moldhaving a longitudinal cavity conforming to the predetermined shape of the stack of refractory metal members, inserting the stack of refractory metal members into the longitudinal cavity of the mold, preheating the mold having the refractory metal members therein, casting a molten metal having good electrical conductivity into the preheated mold cavity about the refractory metal members and the woof wires to bond the mold, metal members and woof wires into a unitary body, and severing the unitary body containing the refractory metal members and the woof wires perpendicular to the refractory metal members into contact members of predetermined size, the section of the mold severed forming a circumferential reinforcement for the cast metal of the contact members.

4. The method of making reinforced electrical contact members comprising, in combination,

metal selected from the group of silver, copper a and their alloys, within the longitudinal cavity to bond the preheated mold and refractory inserts into a whole, and thereafter severing the mold containing the refractory metal inserts in the cast metal through its cross-section into contact members of predetermined length, the section of the mold severed forming a circumferential reinforcement for the cast metal containing the refractory metal insert.

2.-The method of making electrical contact members with refractory metal inserts .to resist heat and impact" deformation comprising providing a mold with a longitudinal cavity, the mold being of metal having predetermined reinforcing characteristics, placing a plurality of elongated, substantially uniformly spaced refractory metalmembers of substantially the same length as the longitudinal cavity witbin'the longitudinal cavity of the mold, preheating the mold and refractory metal inserts contained therein, casting a molten metal having goodelectrical conducting proper- ,ties in the preheated mold and about the refrac- 'spacing'a plurality of elongated refractory metal members selected from the group of tungsten and molybdenum in substantially parallel relation. by means of woof wires disposed in spaced relatron along the refractory metal members, rolling the spaced refractory metal members into a stack while maintaining the members in spaced parallel relation to one another, providing a mold having a longitudinal cavity conforming to the shape of the stack of refractory metal members, the mold being of metal having predetermined reinforcing characteristics, inserting the stack of spaced refractory metal members into the cavity of the mold, preheating the mold having therefractory metal members therein, casting a molten metal selected from the group of silver, copper and their alloys into'the preheated mold cavity about the refractory metal members and the woof wires to bond the mold, metal members and woof wires into a unitary body, and severing the unitary body containing the refractory metal members and woof wires perpendicular to the refractory metal members into contact members of predetermined size, the section of mold severedfo'rming a circumferential reinforcement for the cast metal of the contact members.

- JAMES K. ELY. 

